The use of lactoferrin in the field of dental health

The oral cavity provides a rich environment for the most diverse and stable microbiome in the human body [1]. The oral flora, like the intestinal microbiome, is an essential part of the human innate immune system. The microorganisms located there determine the balance between pathological and physiological states, which can have both local and systemic effects [2].
Depending on factors such as nutrition, age and saliva flow, pathogens can tip the balance of flora. The resulting microbial dysbiosis can lead to problems such as caries, gingivitis and periodontitis.
But it goes further. Studies have shown that the oral microbiome can also be directly associated with the development or deterioration of systemic infections, adverse pregnancy outcomes, cardiovascular diseases, diabetes mellitus and autoimmune diseases [1,3]. 
The largest group of microorganisms in the mouth are the bacteria which can attach themselves in so-called biofilms.  Plaque on teeth is a key example of this [4]. Bacteria within a biofilm are significantly more resistant to antibiotics, antibodies and antimicrobial peptides [5].
Oral bacteria can ferment sugars and carbohydrate-rich foods. This reduces the pH within the biofilm, and pathogenic bacteria such as Streptococcus mutans can gain the upper hand. These bacteria produce acids which can demineralise the tooth surface and thus lead on to caries [6,7].
Over time, the plaque layer can itself mineralise and become tartar.  As a result, gingivitis often arises, one of the most common diseases of the mouth [8].  Chronic gum inflammation can progress to periodontitis with the participation of gingivitis-inducing bacteria such as Porphyromonas gingivalis. In recent years, the relationship between periodontitis and systemic diseases has become increasingly clear. In particular, Porphyromonas gingivalis is found in atherosclerotic plaques [9]. 
The innate immune system provides numerous defence components to prevent the penetration of pathogens into the body via the oral cavity. These include the mucosal barrier, as well as individual proteins located in the body fluids, such as lysozyme and lactoferrin [10].
In view of the diversity of microorganisms, and the sensitive balance between these species, therapeutic intervention in the oral cavity poses a major challenge.  
Although we have many antibacterial substances, very few are able to dissolve a bacterial biofilm. Often, like dental plaque, this biofilm can only be physically removed.  It has already been shown that biofilms play a role in many diseases, from cancer [3], back pain [11,12], Alzheimer’s [13], asthma [9], to rheumatoid arthritis [9,14].
Lactoferrin, however, demonstrates a very efficient clearing of biofilms, even of multi-resistant bacteria, such as Pseudomonas aeruginosa and other oral pathogens [15].
A 2018 review examines the role of lactoferrin in the treatment of various oral and maxillofacial diseases [2]
Antibacterial effects
Lactoferrin showed very good effects against Streptococcus mutans, the main cause of caries, both during attachment, and in the formation of biofilms.
In the case of periodontitis, which is mainly initiated by the gram-negative bacteria Porphyrornonas gingivalis and Prevotella intermedia, lactoferrin was effective against both bacterial strains, albeit by slightly different mechanisms of action.
Antifungal effects 
Candida albicans is the most common fungus in the oral cavity and can trigger various systemic and local disease events, such as oropharyngeal candidiasis and systemic candidaemia. Lactoferrin was very effective in inhibiting the growth of Candida albicans as well as less severe disease progression.
Antiviral effects
One of the most common viral infections of the oral mucosa occurs due to the Herpes virus. After the primary infection, it remains in the body and the infection can flare up again when provoked.  Lactoferrin can intervene here by inhibiting how the virus binds to the surface of the host cell, as well as it’s replication and cell-to-cell propagation.
Another common virus, the Epstein-Barr virus (EBV) often also affects the oro-facial region. Symptoms such as an inflamed throat, swollen lymph nodes and a rash can be found in the head and neck area.  If the host’s immune system is already weakened, serious complications such as viral meningitis, encephalitis or optic neuritis can also occur. Lactoferrin can prevent EBV from attaching and penetrating the host cell and effectively inhibit cell transmission.
The Coxsackie virus A16 (CA16) causes “hand, foot and mouth disease” (HFMD). Studies have shown Lactoferrin has an inhibitory effect in the first phase of the infection.  The same is the case for the humanpapilloma virus (HPV).
Further therapeutic applications of lactoferrin for oral health
  • Dry mouth
  • Bone regeneration in the vicinity of implants
  • Prevention of inflammation in the implant area
A double-blind, randomised intervention study in 2019 investigated the use of a toothpaste containing enzymes and proteins, including lactoferrin.  The composition reflected their natural presence in the saliva, with a view to improving the health of the gums [16].  Many components in saliva belong to the humoral part of the innate immune system, and it plays an important role in maintaining bacterial equilibrium in the oral cavity.  After 4 weeks, it was shown that both plaque formation and the gingival index were significantly reduced.
The oral cavity and its environment can be affected by various infections and pathologies. The authors of the aforementioned reviews recommend lactoferrin as a therapeutic agent in the field of oral health.  It has a wide range of applications without the development of side effects and/or resistance.